Electric furnace



March l0. 1925.

H. A. MULVANY ET L ELECTRIC FURNACE Fl'e'd Oct. 5, 1921 2 Sheets-Sheet l *fill- TTORNE Y H. A. MULVANY ET AL ELECTRIC FURNACB Much 1o. 1925. l 1,529,368

Filpd. oct. s'. 1921 z'sneets-sneet 2 ATTORNEY.'

Patented Mar. 10, 1925.

UNITED STATES PATENT 'ori-lcs HARRY A. MUIANY AND HARRY E. KENNEDY, OF BERKELEY, CALIFORNIA.

ELECTRIC rUnNAcE.

Application ledctober 5, 1921.

To' all whom t may concern.'

and `HARRY E. KENNEDY, citizens lof the United; States, residing at Berkeley, in the countyof Alameda and State of California, have invented new and useful Improvements in Electric Furnaces, of which thefollowing is a specification.

This invention relates to an electric furnace, landespecially to a method of supporting the electric heating elements therein.

The advantages of electricity in heat production for industrial applications; for instance in furnaces, heaters and the like, are so numerous and so generally appreciated that a summary or a rehearsal of them is though unnecessary. -It would be anticipated that this method of heat production would be particularly 4advantageous when cnanielling furnaces and the'like are considered as uniformity of temperature, ease of control, absence of combustion products, and durability are the prime requisites of ,an enamelling furnace. l

'In the construction of an electric furnace or mulile kiln, it should be clearly realized that the factors upon which success depends are as follows: That the furnace must have adequate heat insulation; lthat heat must be generated over the entire.inner surface ofthe furnace uniformly; that the electrical parts, and particularly the heating elements, must be so disposed as'to prevent contact with the waresor articles to be enamelled, and that the temperature of the electric elements should exceed the temperature of the kiln by as small an increment as possible.

The roblem of insulation is readily solved. arious high class insulating materials are on the market and sufficient thickness of walls will reduce radiation and conduction losses to a minimum. l

The disposition of several electric heating elements over the entire surface of the kiln, including the arch and the floor` without interfering with their free radiation into the kiln, is not easily attained. It has been common practice to sustain and protect electric elements in varying forms of kilns by means of a refractory muffle. This arrangement has the very serious handica of restricting the heat flow between the e ectric elements and the kiln. vTherefore an excessive temperature results in the element and since `the most durable material known for high temperaturesl is not stable over 2000 deserial Np. 505,496.

grees Fahrenheit, such a method seriously diminishes thelife of the furnace and particularly theaelements. Also such refractory covering or inutile, unless made exceedingly thick, will not stand the continued jarring of heavy articles continually dropped thereon.

The object of the present invention is to generally improve and simplify furnaces of the character described, and especially to provide a furnace so constructed that adequate heat insulation may be obtained; that heat will be generated over the entire inner surface uniformly; that the metallic elements or resistere will be so disposed as to prevent Contact with the wares', and that the difference in temperature between the furnace and the electric resister elements shall be exceedingly small. t

'Another object of the invention is to provide a special form of interlocking brick constructed of refractory material, which when properly laid up to the form of any muie or furnace will support an element either of the wire or ribbon type; said bricks further when laid forming a zigzag slot Within the furnace chamber in which the elements are disposedpand supported.

Further objects will hereinafter appear.

The invention consists of the parts and the construction, combination and arrangement of parts as hereinafter more fully described and claimed, lhaving reference to the accompanying drawings, in which- Fig. 1 is a cross section of the furnace.

Fig. 2 is a central, vertical, longitudinal section.

Fig. 3 is a plan view of two bricks showing the position of the heating elements with relation to the same.

' Fig. 4 is a cross section on line 4-4., Fig.` 3.

Fig. 5 is a perspective view of one of the bricks. Y

Referring to the drawings in detail, A. indicates in general a furnace of suitable design and construction, 2 a furnace chamber formed within the same. This furnace chamber, including arch, sides and floor, is built up of a special form of refractory brick, such as illustrated in Figs. 3, 4 and 5; certain of the bricks being arched or key bricks to form a rigid roof construction and to insure perfect design and alignment of the arch. All bricks are identical in construction; the only difference being that the bricks employed in the arch are tapered in A. cross sectlon to take care of the arch tructure. The bricks when placed in position form a floor 3, sides 4:, and an arch or .roof 5. These are `well insulated with the best grade of insulating material and the entire structure is supported by an exterior shell in the usual manner as indicated at B; The exterior shell, known as the furnace frame,

may be designed to suit varying conditions.

\ It should however be constructed of exceptionally heavy cast-iron and ribbed so as to give maximum strength and to prevent dis.- tortion.

vided'and peep-holes may beformed adjacent the door, or at any other convenient point for observation of the .interior of the furnace.

The features so far described are of no material importance as far as the present invention is concerned as it is obvious that the method of insulation, or material employed, and theparticular design of the exterior furnace frame, may be changed to suit varying conditions. Y The present invention is particularly limited to the interior design of the furnace, and especially to the method of supporting and retaining the metallic re\ sisters or heating elements. With this* object in view a special form of' brick, as alreadv stated, is em loyed. The brick is long and n arrowlias sliown in Figs. 3, 4 and 5, and is provided with a head at each end; the heads being illustrated at 6 and 7 respectively. Formed as an'integral part of the head 6 is a centrally Vdisposed web 8, the sides of which present tapering Walls or refleeting surfaces as will lhereinafter be described. The central web is separated with relation to the head 7 bythe formation of a gap 9, anda recess is formed at the 'lower end of the web, as at l0; a similar recess extending crosswise of the brick being formed in the head 7, as at 11.. All of the bricks employed are identical in design and construction,l but they are. reversed with relation to each other when placed in position in the furnace. This reversing of the bricks is clearly illustrated in Fig. 3. r.he recesses 10 and 11 formed in each brick serve as a support for the metallic resister or heating element which is preferably of the ribbon type, and as the bricks are reversed when placed, it is obvious that a support will be provided for the heating element at each en The reversing of the lbricks and Heavy cast-iron arches extending l over the arch and bolted to the side plates the formation of the webs 8 with their taper- I ing side walls 12 is of great importance as it forms a zigzag channel, as indlcated at 13, foi' the reception of the heating element 14, which is ybent to form a zigzag or similar shape. It should further be noted that the channel formation appears on the inner side i.

or surface ot' the bricks, and that direct communication is formed between the furnace chamber 2 and the zigzag channels. It may further be stated that the depth of the channels formed between the bricks is such that the heads 6 and 7 and the webs 8 of the respective bricks. Will extend a considerable distance beyond the -heating elements, thus protecting them against contact with the lWares placed in the furnace. lIt should beI remembered that the fioor, ,sides and the arch, are built up of the brick illustrated, and that continuous channels will therefore be formed around the entire interior surface. The bricks being placed end for end, as illustrated in Fig. 2, will form a series of annular continuous channels and each channel being provided for the reception of an element. c y

Electrically, the construction -consists of a suitable number of circuits in multiple, one- -half of which may be located in the arch ofl the furnace, and one-half in the floor, so that in effect the heating area consists of a plurality of rings encompassing the kiln. These circuits are connected to. bus-bars which are in turn attachedy to the secondary side of a variable voltage transformer. In actual practice energy at' approximately 2300 volts is employed. By means of inagnetic switches connected to transformer taps, it is possible to quickly vary the furnace input. The arrangement permits of very accurate adjustment of the current iow, thus suiting the needs of the individual enameller, etc.

The heatin elements, as previously stated. are rib yon shaped in cross section and zigzag in formation. They consist of heavy nickel chromium metal and as they are placed in the grooves or channels formed between the refractory bricks, it is obvious that their heating efficiency should be great due to the large surface presented, and also because the bricks have a high dielectric strength when the average working temperature is considered, and they at the same time possess the quality of a good heat conductor under such conditions. Each brick furthermore presents a pair of inclined reflecting surfaces which materially assists in projecting or radiating the heat developed. 'ln fact each brick may be glazed or other wise treated to further promote sufuh effect. Direct communication between the heating elements and the furnace chamber is of great importance as interference with free radia`1 tion is positively avoided.

llO

I' will be comparatively short.

electric furnaces, employing metallic resistels, it becomes a necessity when successful operation is considered that the difference in temperature of the furnace and the electric resister clement shall be small, that is in a furnace designed to operate at 1800 degrees Fahrenheit, the temperature of the metallic resister should not exceed 1900 degrees Fahrenheit at any point. Due to the physical properties of metallic resisters now obtainable, it is obvious that if 'the foregoing temperature, to-Wit, 1900 'degrees Fahrenheit, is exceeded, the life of the element The present construction allows an almost'unrestricted radiation intottheiurnacechambers; in fact actual practice has determined that the temperature of the elements at their hottest points does not exceed the furnace chamber temperature by more than degrees Fahrenheit and as the average furnace temperature seldom exceeds 1750 degrees Farhenheit, it can readily be seen that the element temperatures are very conservative and productive to long life. v

In' most furnaces in use today, it. has been common practice to sustain and protect the electric elements by means of la refractory muiile. This arrangement has a very serious handicap of restricting the heat flow bctween the electric element and. the kiln or furnace chamber, therefore excessive temperature 'results in the element, and since.

the most durable material known and in use today, to-wit, nickel chromium, is not stable above 2000 degrees Fahrenheit, such covering or protection of the elements will obviously rapidly diminish the life of the elements. Also such refractory covering, unless made exceedingly thick, will not stand the continued jarring of heavy articles dropped on their red hot surfaces.

In the present instance by the use of the specially designedr brick, it is possible to dev sign a furnace for any use desired; the

bricks when properly laid permitting elements of either wire or ribbon type to be employed, and as the elements are laid both in the floor, sides and arch of the furnace, it can readily be seen that uniform heating will be obtained. The zigzag channels formed between the bricks are so deep that the elements are amply protected, and the ware or other material to be treated in the fur na.e can therefore be freely inserted and removed without danger of contacting with the elements. The special brick employed furthermore permits the elements to be readily inserted or removed whenever desired and accidental release or removal is pre-- vented by filling the gap 9 with a temporary plug of lire-clay or the like which rapidly liardens when in place.

The furnace can be so Well insulated that the Workersv are in comparative comfort, and as the furnace floor is built upon a solid foundation, it is obvious that sagging or distortion thereofcannot take place. This feature cannot be too strongly emphasized;

"for instance Where oil fire furnaces are employed continual sag ing of the ioor and consequent warping o the bricks takes place and often results in distorted ware and continual furnace repair, this being due to the excessive heat to which the Hoor is exposed.

The life ofthe brick Work in the present instance is unlimited because the heat is generatedv directly within the walls of the kiln and not exterior thereof, therefore, it is not necessary to maintain the excessive temperatures which are so disastrous to brick work. The speed with which operating temperaturesl yare reached, is another valuable feature as actual experience has shown that the furnace may readily be brought from room temperature to 1700 degrees Fahrenheit in five hours Without an abnormal expenditure of energy, and Without causing excessive expansion `to the brick work which might prove destruct-ive.

Having thus described our invention, what we claim and desire to secure by Letters Patent is- 1. In a furnace of the character described, a brick lining, each brick of said lining consisting of a base portion, a head at each end thereof, a central web extending between the head members and forming apart of one of -the head members, said web being separated and notched With relation to the opposite head member, said bricks when placed in the furnace being alternately reversed, said webs when the bricksare reversed forming zigzag channels between the bricks, and a heating element of zigzag format-ion adapted to be placed in the channels and supported at opposite ends by the notched portion of each brick.

2. ln a furnace of the character described, a brick lining, each brick of said lining consisting of a base portion, a head at each end thereof, a central web extending between the head members and forming a part of one of the head members, said web being separated and notched with relation to the opposite head member, said bricks when placed in the f urnace being alternately reversed, said webs when the bricks are reversed forming zigzag channels between the bricks, and a heating element of zigzag formation adapted t0 be placed in the channels and supported at opposite ends by the notched portion of each brick, the side Walls of said webs being tapered to form reflecting surfaces.

3. In a furnace of the character described, a brick lining therefor composed of bricks having recesses formed on their side faces and in one end which, when the bricks are ing to a point adjacent the opposite head, a.

recess formed in each brick between said last named head and the web, said bricks being reversed with relation to eachother when laid in the furnace, and said webs forming channels between the bricks,l and heating elements disposed in said channels and supported at opposite ends by the recesses formed between the webs andthe heads of each brick.

5. vIn a furnace of the character described, a heating chamber, a lining brick for the oor, sides and'roof arch of said chamber,

' said brick comprising a basel section and a head member formed on each end thereof, a narrow web extending from end to end of the brick and forming a part of one head and the base portion, and a recess formed between the web and the other` head.

6. In a furnace of the character described, a.heatin chamber, a lining'brick for the Hoor, si es and roof arch of saidvchamber,J

said brick comprisingr a base section and a head member formed on each end thereof, a narrow web extending from end to end of the brick and forming a part of one head and the base portion, and a recess formed between the web and the other head, the sides of the web presenting tapering walls.

7. In a furnace of the character described, a furnace chamber, a refractory lining therefor, said lining having a continuous zigzag shaped groove formed in its' inner face, a zigzag shaped heating element adapted t0 he received by the groove, and inwardly projecting knobs formed in the zigza groove to support the heating element an to permit removal thereof without'disturbing the refractory lining.

8. 'In a furnace of the character described, a furnace chamber, a permanent refractory lining therefor, said lining having a continuour zigzag shaped groove formed in its inner face, a zigzag shaped heating element adapted to be received by the groove, and means for retaining the element in the groove, said zigzag groove being tapered in vcross-section so that the side faces of the groove may present angularly disposed reflecting surfaces.

9. In a furnace of the character described, a furnace chamber, a permanent refractory lining therefor, said lining having a continuous zigzag shaped groove formed in its inner face, a zigzag shaped heating element adapted to be received by the groove, and inwardly projecting knobs formed in the zigzag groove at opposite ends thereof to supportthe heating element and to permit removal thereof` without disturbing the refractory lining.

HARRY A. MULVANY. HARRY E. KENNEDY. 

